1. Field of the Invention
The invention relates to a multi-part longitudinal shaft for motor vehicles, for transfer of a torque, particularly for the drive train of a motor vehicle. The shaft consists of two or more shaft sections and one rotary joint that connects the two shaft sections. The joint can be a homokinetic joint.
2. The Prior Art
Such longitudinal drive shafts are generally known and serve to transfer torque and are configured in such a manner that in the event of a crash, i.e. a frontal impact accident or a crash in the longitudinal direction of the vehicle, the longitudinal drive shaft is shortened in the axial direction, in order to avoid bending and penetration into the interior of the motor vehicle. This precludes injuries to the persons situated in the passenger space, to the greatest possible extent.
For example, in German Patent No. DE 199 43 880 C1, a longitudinal drive shaft having two shaft sections is described, which sections are connected with one another by way of a homokinetic rotary joint. The homokinetic rotary joint comprises an inner joint part that is connected with one of the two shaft sections, so as to rotate with it. The outer joint part is connected with the other of the two shaft sections, so as to rotate with it, and balls held in a cage serve to transfer torque between the inner joint part and the outer joint part.
The diameter ratios of the two shaft sections are selected in such a way that after destruction of the homokinetic rotary joint, in the event of a crash, the two shaft sections are supposed to move into one another, in telescoping manner, and essentially without force, if the displacement path of the homokinetic rotary joint that is maximally permissible in the axial direction is exceeded.
Displacement of the parts into one another is reliably guaranteed by the different dimensioning of the functional parts of the drive array in question, in order for them to telescope relative to one another. However, a significant force is required to initiate this process of telescoping, and there is no guarantee that the longitudinal drive shaft will not bend.
German Patent No. DE 10 2005 029 754 B4 describes a multi-part longitudinal shaft for the drive train of a motor vehicle, which consists of two shaft sections that are connected with one another by way of a rotary joint. The shaft sections are configured with different diameters, so that these shaft sections can be pushed into one another. In the first shaft section, a protective element is disposed, which accommodates the inner joint part at least in part, after the rotary joint is broken down, and is supposed to guide it into the first shaft section. The protective element has an attachment section for support relative to the first shaft section, and an accommodation section for accommodating the inner joint part. In addition, a planned breaking point is provided in the accommodation section.
Another longitudinal drive shaft for motor vehicles, which consists of two or more shaft sections that are connected with one another by way of an intermediate shaft or a journal, are described in German Patent Application No. DE 10 2007 015 074 A1.
The intermediate shaft or the journal is the carrier of a center bearing. In the direction toward the first shaft section, the intermediate shaft or the journal are connected by way of a joint that is fixed in the tube, and the parts that are displaced in the event of a crash, are configured in such a manner that these can also be pushed into one another and guided in one another.
The joint that is provided in the case of this longitudinal drive shaft is configured as a homokinetic displacement joint that consists of an outer joint ring, a ball hub, balls that are disposed to move in ball grooves leading from the outer joint ring and the ball hub, as well as a cage. The homokinetic displacement joint is sealed, in the direction of the one shaft section, with a sealing cap and sealing bellows. A closure lid configured as a guide and securing element is assigned to the homokinetic displacement joint relative to the other shaft section and projects into the interior of the tube, which element is configured with planned breakage points.
The solutions that are presented reliably guarantee telescoping of the functional parts of the longitudinal drive shaft in the event of a crash, but even in these solutions, there is the risk that under certain circumstances, the shaft sections will not telescope into one another completely. Thus, there is the risk that the outer shaft tube will tear open, as the result of penetration of the other shaft tube, due to bending moments that occur, and thus the longitudinal drive shaft is only pushed partly into itself.